1. Field of Invention
The present invention is related to an optical device and a fabrication method thereof. In particular, it is related to a CMOS image sensor and a fabrication method thereof.
2. Description of Related Art
Because CMOS image sensor (CIS) is compatible with CMOS technology, CIS can be easily integrated with other peripheral circuits on the same chip, thus greatly reducing the cost and consumption power of the image sensor. Accordingly, during recent years, the importance of the CMOS image sensor keeps increased and CIS has become dominant over charge coupled device (CCD) in the lower-priced market applications.
U.S. Pat. No. 6,861,686 discloses a structure of a CMOS image sensor and a fabrication method thereof for resolving the issues derived from the use of copper in replacement of aluminum for the fabrication of interconnect.
However, certain problems are still unsolved by U.S. Pat. No. 6,861,686. For instance, the external light passes through the lens, the color filter, into the metal interconnect line, and is then collected by the photodiode. However, as the external light passes through the light passageway in the metal interconnect line, the external light may be absorbed by the dielectric layer, protective layer, or other thin film layers on the surface of the light passageway if it does not directly reach the photodiode. As a result, the photosensitivity of the CMOS image sensor is reduced.